Generating Terrain

There are two general approaches to generating synthetic terrain, either for use in a game or for rendering into pretty images (or both). One is to use actually measured data of real portions of the earth (or other planets), and another is to synthesize your own data. Either way you end up (typically) with an array of elevations, known as a heightfield (or displacement map, or depth map).

For real data, you'll typically get a DEM (digital elevation map) in the USGS (United States Geological Survey) format, or in formats compatible with specific GIS packages.

For synthesizing your own, you can do one of these:

Draw your own
Since a heightfield is so much like an image, many people "draw" landscapes using paint tools. Zero is the lowest height, and 255 (for an 8-bit image) is the highest. This method gives you the most control over your landscape, but you're limited to what you draw.
Use a program
There are several programs which can generate and/or render height fields. Once again, the terrain is generated beforehand, unless you make an arrangement with the program's author to distribute the terrain tool with your program.
Roll your own
Develop some code, either as a standalone utility or as a component of your program, which can generate terrain. This is the most flexible and potentially space-saving method, since your terrain can be represented by formulas and code instead of multiple megabytes of storage, but there is a time tradeoff. There are many, many methods of generating terrain on-the-fly. I've grouped the ones I know about into the following categories:
Subdivision ("plasma")
Composition of functions
Frequency synthesis
Wavelet synthesis
Noise synthesis
Faulting and/or Collaging
"Growing" or "Evolving"
Physically-based or -inspired methods
Plate tectonics
Erosion and hydrology
Other ad hoc methods
Mix and match
An interesting hybrid is mixing some actual, predrawn, or pregenerated terrain data with terrain generated on-the-fly. This would typically be done to enhance the predrawn terrain with additional detail.

For rendering your terrain (if you are not already using a rendering package such as POV-Ray), the 3D Engines List provides pointers to a large number of realtime rendering packages, many of which are cheap or free. There is a subsection specifically for Landscape/Voxel engines which would be of particular interest.

Some tricks

Any of these fractals can be used for cloud patterns, although some may look better than others.

Try doing some post-processing or digital filtering on the heightmap to get some interesting effects.

Try calculating two of these fractals, using one for altitude and one for rainfall, to cheaply calculate "climate". [Thanks to Stan Shebs, developer of xconq.]

Most of these algorithms use a uniform random distribution or constants. Try some other distributions (e.g. Gaussian normal) and see if the results are more to your liking.

terrain bookstore Looking for books about creating landscapes on the computer? You can find some here!

Other terrain pages [Under construction]

Planetside, a project in synthesizing realistic terrain
Generating Random Fractal Terrain, by Paul Martz
Terrain references by the author of 'Wilbur'
Landscape Series Index - articles about landscapes in games

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